Alpha hydroxy acids (“AHAs”) are known to be useful in skin care compositions for treating various skin conditions, including rhytids (i.e., wrinkles), xeroderma (i.e., dry skin), hyperkeratosis, ichthyosis, and discoloration. Specifically, AHAs that are short chain carboxylic acids, such as glycolic acid and lactic acid, are preferred in cosmetic compositions due to the AHAs ability to penetrate skin. In particular, the bioavailability of short chain AHAs stimulates cellular activity in the epidermis and dermis, as well as increases desquamation of the outer layers of the epidermis to help alleviate and treat the skin conditions above. Furthermore, short chain AHAs can aid and stimulate collagen synthesis, which further helps reduce rhytids, while improving skin elasticity and firmness.
However, a major problem with using AHAs in skin care compositions is the fact that AHAs are acids, which can lead to skin irritation. And while using AHAs for their acidic properties may be desirable in certain applications, such as for skin peel applications, the acidity of AHAs can have detrimental and undesirable effects for more daily and routine applications.
In order to reduce the irritation associated with using AHAs in skin care compositions, other compounds can be added in an attempt to make the overall skin care composition less acidic. For example, U.S. Pat. Nos. 5,886,042 and 5,385,938 discuss adding an amphoteric or pseudoamphoteric compound with the AHAs to try and raise the overall pH of the cosmetic composition. However, not only do these compositions require an additional component, such as amino acids and imidazoline compounds, which may not be desirable for a particular composition or use, but this strategy also does not address the underlying issue regarding the acidity of the AHAs. Rather, by attempting to balance the AHA with another compound, the acidity of the AHA is merely being masked and not reduced. By not addressing the problematic acidity of the AHAs, skin irritation and intolerability can persist, especially in users with sensitive skin.
In addition to problems associated with the acidity of AHAs, skin care compositions in the field generally have problems sustaining relatively long-term stability, while also allowing sufficient penetration of the active ingredient into the skin. Stability problems can occur based on a variety of environmental factors, including changes in temperature and humidity during processing, shipping, storage, and use, as well as chemical factors within the compositions, including the miscibility or homogeneity of the various components. In this respect, less stable compositions can be more acidic and can potentially become more acidic over time due to masking components becoming diminished or separating out of the compositions, which further exacerbates the irritability of the compositions.
Accordingly, there remains a need in the art for skin care compositions that have reduced acidity and potential irritability, while also having sufficient stability and penetration properties. As such, there remains a need in the art for skin care compositions having at least one cyclic diester, such as at least one cyclic diester of an AHA. Moreover, there remains a need in the art for skin care compositions having the aforementioned cyclic diester and at least one polar non-aqueous solvent.